Taking a large hit/toke from a bong/bubbler/vaporizer holding the smoke in the person's lungs while taking a shot of liquor then chugging a beer; finally doing a line and blowing out the smoke.
*Almost impossible*

"that fool did a Grand Slam last night and straight up died; but we all thought it was ill to watch!"

Okay for this you need 4 gentlemen and a chick. A party may be a good place for this. The first three gentlemen need to make out with the chick. They each get to "first base." The bases are loaded as the "runners" advance. Finally the fourth gentleman approaches the chick and proceeds to have sexual intercourse with her. Once he "gets all around the bases" by this act he has "hit a grand slam home run." Or simply a "grand slam." The remaining gentlemen burst into the room and many hi-fives are exchanged while they all yell, "Grand Slam."

Hey I hit a Grand Slam with this chick and some help from my best buds last night.

Series of the following sexual positions performed in succession while maintaining continuous penetration: missionary then flipping to cowgirl then spinning around to reverse cowgirl and finishing with doggie style.

My boyfriend and I were so inspired by our team's gland slam that we celebrated with our own grand slam!